With the expansion of cellular and other wireless communication services, there is a growing requirement for antennas suitable for communications with cellular telephones and other mobile user equipment. These antennas are typically provided in fixed installations on buildings or other structures in urban and other areas. The characteristic of the use of a large number of contiguous cell coverage areas of relatively small size, particularly in urban installations, results in the need for installation of large numbers of antennas. Relatively low power operation is generally involved, however, the need to provide reliable communications service to a population of users moving through coverage areas with varying transmission characteristics places special requirements on the antennas.
While many types of antennas are available for these applications, prior antennas typically have one or more of the following undesirable characteristics: limited performance, high cost, high component count and assembly labor, signal path connections subject to generating spurious intermodulation effects, limited reliability, high susceptibility to lightning damage, bandwidth or beamwidth limitations, high design and fabrication costs for reconfiguration for different applications, limited flexibility for beamwidth or beam tilt variations, unattractive visual characteristics, large front to back dimensions and special tower or other mounting requirements.
Some antenna characteristics are particularly significant in cellular and similar applications. Contacts or physical connections in the signal path can, over time, degrade and result in spurious intermodulation effects which are unacceptable in cellular applications. Achieving high performance and reliability with low cost places emphasis on a low component count and ease of production and assembly. Adaptability to a variety of installations and operating requirements is enhanced by a construction with flexible design aspects. Adaptability to beam forming and active antenna beam steering and null control techniques is facilitated by antennas providing multiple beam capabilities. Particularly in urban locations, antenna esthetics and the capability of enabling unobtrusive antenna placement on the sides of buildings are significant objectives. Susceptibility to lightning damage can place systems out of service and result in high costs of antenna replacement.
Objects of this invention are, therefore, to provide new and improved types of slot array antennas, and antennas having qualities which favorably address one or more of the previously identified characteristics.